The general guidelines as I read them, state that the grate should be about 24 inches above the fire. The barrels are 34 to 35" high, the bottom of the barrel is recessed about 1", and my charcoal box is raised about 2 1/2 inches. That leaves 31 1/2" from the bottom of the fire to the top of the drum. My charcoal box is 9" high, so I went to halfway, leaving 27" to the top. Putting the grate 24" above that leaves 3" for meat. Insert joke here. I think I finally measured down 6" for my grate. I'd love to do the dome thing, get another grate. You just need a table, upon which to store the top grate whilst you work the bottom grate. Or something.
And what Ralph said about runaway temps is SO true!! If I go in there, pull off a roast, wrap it, put it back, get the next one, wrap it....yeah. Flashover starts in about 80 seconds, and 10 seconds after that, you have a roaring fire. Half a minute later, the temps in the barrel are at 350-375. Looks like a NY alley in the winter.